The toxicity of acetaminophen will be studied in newborn and young rats of various ages. The drug will be given and the following parameters measured: serum enzymes, hepatic glutathione, hepatic morphology and hepatic binding of drug metabolites. In other studies, the tissue concentrations of acetaminophen and each of its metabolites will be measured in mice given toxic doses of the drug along with various agents known to modify acetaminophen hepatotoxicity. These studies will be conducted in an effort to gain more information on the relationship between drug metabolism and drug toxicity.